A number of cellular proteins have been demonstrated to occur at increased levels in body fluids of subjects with different types of cancer. The increased levels of such proteins in cancer subjects provide diagnostic and prognostic assays for the presence of cancer. For example, elevated serum levels of prostate specific antigen (PSA) is frequently used as an indicator of the presence of prostate cancer in men.
Autoantibodies to normal or modified cellular proteins are known to be produced by patients in certain diseases such as autoimmune diseases and cardiovascular-related disorders, in some cases even before the disease has produced overt symptoms. There is also increasing evidence for a humoral immune response to cancer in humans, as demonstrated by the identification of antibodies against a number of intracellular and surface antigens in patients with various tumors (Gourevitch et al., 1995, Br. J. Cancer 72:934-938; Yamamoto et al., 1996, Int. J. Cancer, 69:283-289; Stockert et al., 1998, J. Exp. Med. 187:1349-1354; Gure et al., 1998, Cancer Res. 58:1034-1041). For example, somatic alterations in the p53 gene elicit a humoral response in 30-40% affected patients (Soussi, 1996, Immunol. Today 17:354-356). In some instances, the detection of anti-p53 antibodies can predate the diagnosis of cancer (Lubin et al., 1995, Nat. Med. 7:701-702; Cawley et al., 1998, Gastroenterology 115:19-27). U.S. Pat. No. 5,405,749 discloses a method of screening for cancer-associated retinopathy autoantigen and testing a patient's serum for autoantibody to the autoantigen. In addition, increases in relative rates of synthesis of major cytoskeletal proteins have been observed on the surface of leukemic cells and of lymphocytes transformed by mitogens and Epstein-Barr Virus (Bachvaroff, R. J. et al., 1980, Proc. Natl Acad. Sci. 77: 4979-4983).
The majority of tumor derived antigens that have been identified and that elicit a humoral response are not the products of mutated genes. They include differentiation antigens and other gene products that are overexpressed in tumors (Old and Chen, 1998, J. Exp. Med. 187: 1163-1167). It is not clear why only a subset of patients with a tumor type develop a humoral response to a particular antigen. Factors that influence the immune response may include variability among individuals in major histocompatibility complex molecules. It is also possible that proteins may become immunogenic after undergoing a post-translational modification, a process which may be variable among tumors of a similar type.
Lung cancer is the most common cancer in the United States and accounts for over one fourth (28%) of cancer deaths in the US (Travis et al., 1996, Cancer 77:2464-2470). A number of molecular alterations including c-myc amplification, Ki-ras or p53 mutations have been identified that may affect tumor behavior (Mao et al., 1994, Cancer Res 54:1634-1637, Mills et al., 1995, J. Natl. Cancer Inst. 87:1056-1060, Gao et al., 1997, Carcinogenesis 18:473-478). Serum autoantibodies against the product oncogenes and tumor suppressor genes, such as c-myc (Ben-Mahrez et al., 1990, Int. J. Cancer 46:35-38), c-myb (Sorokine et al., 1991, Int. J. Cancer 47:665-669), c-erbB-2 (Pupa et al., 1993, Cancer Res 53:5864-5866), ras (Takahashi et al., 1995, Clin. Cancer 1:107) and p53 (Peyrat et al., 1995, Lancet 345:621-622; lizasa et al., 1998, Cancer Immunol. Immunother. 46:345-349), have been reported in patients with various malignant diseases. Autoantibodies against L-myc oncogene products have been reported in 10% of sera from patients with lung cancer (Yamamoto et al., 1996, Int. J. Cancer 69:283-289). Serum autoantibodies against p53 have also been detected in sera of non-small-cell lung cancer patients (NSCLC) (lizasa et al., 1998, Cancer Immunol. Immunother. 46:345-349). Elevated serum titers of anti-p53 autoantibodies were present in approximately 20% of the cases of (NSCLC), and the occurrence of these autoantibodies reflect the presence of p53 mutations and p53 over expression (Yamamoto et al., 1996, Int. J. Cancer 69:283-289).
The detection of autoantibodies to cellular antigens and the identification of proteins that have elicited autoantibodies has been accomplished using a variety of approaches. For example, Proliferating Cell Nuclear Antigen (PCNA) was first described as a nuclear antigen which bound antibodies from some patients with lupus erythematosus (Miyachi, K., Fritzler, M. J., and Tan, E. M., 1978, J. Immunol 121:2228-2234). It was subsequently observed that resting lymphocytes did not react with the antibody, in contrast to mitogen stimulated lymphocytes which displayed nuclear staining. This ultimately led to the identification of the protein, designated PCNA which is recognized by this autoantibody in lupus (Tan, E. M., Ogata, K., and Takasaki, Y., 1987, J. Rheumatol., 13:89-96). In some other cases, candidate proteins are singled out and investigated with respect to their ability to induce antibodies in patients, as was investigated for p53 (Crawford, L. V., Firm, D. C., Bulbrook, R. D., 1984, Int J Cancer 30:403-408). In addition, a technique called SEREX relies on serological analysis of recombinant cDNA expression libraries to identify tumor antigens (Old, L., et al. 1998, J. Exp. Med. 187:1163-1167). Thus, many approaches have been followed to search for proteins against which autoantibodies may be produced.
Annexins are a family of calcium-dependent phospholipid-binding proteins that are expressed ubiquitously in different tissues and cell types of higher and lower eukaryotes (Benz, J. and Hofmann, A., 1997, Biol. Chem 378:177-183). At least twelve annexin proteins have been identified. Among the many roles suggested for the annexin family of proteins, those implicating the proteins in regulated exocytosis remain the most convincing (Donnelly, S R and Moss S E, Cell., 1997, Mol. Life Sci. 53:533-538). A typical annexin protein is characterized by two distinct features, (i) Ca2+-dependent binding to phospholipids; and (ii) the presence of a conserved sequence element of about 70 amino acids which is repeated four or eight times in a given member of the family. Immunocytochemical studies of annexins have shown that they reside subadjacent to plasma membranes, near calcium-sequestering intracellular organelles (Gerke, V and Moss, S E, 1997, Biochimica et Biophysica Acta 1357:129-154). Physical properties associated with annexins include inhibition of phospholipase A2, anticoagulant activity, binding to cytoskeletal proteins, aggregation of membranes and vesicles and calcium-selective channel activity. Increased levels of annexin have been found to be associated with a number of diseases including multiple sclerosis and experimental neuritis.